CN202546362 discloses an LED (light emitting diode) lamp which i.a. comprises a lamp holder which is arranged at the bottom of a bulb; an LED circuit board arranged in the lamp holder; a vertically fixed LED lamp panel, wherein the LED lamp panel is electrically connected with the LED circuit board in the lamp holder through a rotating member; and a light guide sheet which is overlapped on the luminous surface of the LED lamp panel.
However, the light guide sheet in CN202546362 may reflect part the light emitted by the LED lamp panel back to the LED lamp panel, thus reducing the efficiency of the lamp Especially if the optical function of the light guide sheet is strong, the associated back reflection is increased. This lowers the efficiency of the lamp, which increases the cost of the lamp. Also, the light absorbed by the LED lamp panel increases the temperature of the LED lamp panel, which may reduce the life time of the lamp.